This invention relates to foundation units, and more particularly to a foundation unit which may be shipped in a collapsed state and later elevated to a fully expanded state using attached components of the foundation unit alone, or such components plus additionally added elements.
U.S. Pat. No. 4,377,279, assigned to the assignee of this application, pertains to a foldable steel wire foundation unit such as a box spring for bedding purposes. The foundation unit is composed of a rigid bottom substructure, a flat top wire grid structure, and a plurality of spaced, parallel rows of substantially flat support members extending between the grid structure and the bottom substructure. Because the support members are substantially flat and are hingedly secured to the grid structure and the bottom substructure, the foundation unit can be fully assembled at a factory and then shipped to the customer in a collapsed orientation, with the customer ultimately raising the unit to a fully expanded orientation and locking the structure in place by means of a plurality of oppositely directed struts.
U.S. Pat. No. 4,770,397 is an improvement over the structure of U.S. Pat. No. 4,377,279, and is also assigned to the assignee of the present application. The '397 patent is directed to a different type of wire support member for a foundation unit, in the form of planer wire elements comprising a pair of oppositely oriented sinuous wire segments. The wire elements provide some resiliency, and a foundation unit employing the wire elements is capable of being collapsed for shipping and expanding for ultimate use.
The present invention is intended to be an improvement over those disclosed in U.S. Pat. Nos. 4,377,279 and 4,770,397, the disclosures of which are incorporated herein by reference. Due to the nature of the present invention, which will become more apparent from the description below, auxiliary stabilizers such as struts are unnecessary.